1. Field of the Invention
The present invention relates to the control of airflow direction in a rack of electronic devices, and more particularly to the prevention of hot air recirculation.
2. Background of the Related Art
Computer systems consume power and produce heat as a byproduct of power consumption. In particular, computer systems often include many rack-mounted components in a high-density arrangement, which can produce a considerable amount of heat. Thermal management of computer systems requires removing excess heat to control internal temperatures, which may increase the reliability, performance, and longevity of the equipment. In a rack-mounted computer system, for example, rack-mounted blowers are typically used to generate airflow through the rack to remove the excess heat and cool the components. Innovations in computer technology have resulted in increasing component density and power consumption of rack-mounted computer systems, with a corresponding increase in the amount of heat produced. These increases in power consumption and heat production have heightened the emphasis on thermal management of rack-mounted computer systems.
The arrangement of equipment racks in a datacenter can have a dramatic effect on the performance of the cooling system. Racks are commonly arranged in an organized hot-aisle/cold-aisle layout to minimize the likelihood of appreciable volumes of heated exhaust air from directly re-entering the racks. A hot-aisle/cold-aisle layout may include alternating hot aisles and cold aisles, with the front of each rack facing a cold aisle and the rear of each rack directed toward a hot aisle. A computer room air conditioner (CRAC) supplies cool air to the cold aisles. The cool air from the cool aisle is drawn into the front of each rack and the heated air is exhausted through the rear of the rack to the hot aisle. The heated exhaust air then recirculates through the CRAC to be cooled and returned back to the cold aisles.
Recirculation of heated air is another issue affecting rack mounted equipment. Rack systems typically house a number of elements having interrelated airflow and heating patterns. Recirculation can be induced in open areas between the rack-mounted equipment, such as in and around empty slots. Ideally, these rack openings are blocked off by bolting blank filler panels to the rack frame. If the blank filler panels are left off, however, the pressure difference created by fans within the rack mounted equipment can force heated exhaust air to travel forward through the rack via a missing panel to the front of the equipment, where the heated air is sucked back into the equipment. Undesirable recirculation of hot air through gaps between components within a rack can also occur as a result of air flow impedance that is associated with use of a rear door heat exchanger.
Recirculation of warm air can cause rack mounted equipment to experience a substantial temperature increase. The additional heat introduced to the equipment by recirculating warm air may cause the equipment to exceed thermal thresholds, particularly if the equipment is operating in a room that is very warm to begin with, or if the amount of heating that takes place within the equipment is substantial. These high temperatures can cause the equipment to shut down or require it to be removed from service. Some portions of rack mounted equipment may experience more recirculation than others, which may interfere with the proper diagnosis of thermal problems. The difference between ambient room temperature air and heated air exiting from the back of rack mounted equipment can easily be 20 to 30° C. or more.